Joining a health club or gym gives you access to a variety of equipment and classes to spice up your workouts, but if you don't like the cost or environment of a gym, you can also get great exercise versatility—and more convenience—by turning your iPhone or iPad into a portable gym, complete with all the classes you'd find at your local gym. Here are a few excellent, inexpensive apps you can use to create a customized fitness program or "gym in your pocket."

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